With heavy rain in today’s forecast, leaving it questionable whether a game can be played at Citi Field, the Mets may have to scrap plans to pitch Matt Harvey and Zack Wheeler in Tuesday’s scheduled doubleheader in Atlanta.

If Thursday’s game against the Cardinals is postponed, Harvey would face the Cubs Friday and make his ensuing start on Wednesday in Atlanta. Wheeler still would make his major league debut on Tuesday, with Dillon Gee on schedule to work the other half of the doubleheader.

According to a club source, manager Terry Collins is leaning toward using Wheeler in the nightcap of the doubleheader.

As for a potential makeup if today’s game is postponed, the Mets and Cardinals have just one common day off for the remainder of the season: June 24. That falls in the middle of a road trip that takes the Mets from Atlanta to Philadelphia to Chicago to Colorado. It would also leave the Mets with scheduled games on 31 consecutive days.

Weather already has been responsible for six Mets postponements this season.

”I don’t think anybody in baseball has gone through what we have weather wise,” Collins said before the Mets’ 5-1 victory over the Cardinals at Citi Field “Now that the schedule is so imbalanced, it eats up days off. Because we’ve had so many days off early it’s not that anybody is tired, but when it gets to be 90 degrees every day and it’s July it’s going to take its toll to where you’ve really got to make sure guys are getting days off to keep their energy up because it’s going to wear them down.”

* Once Wheeler is promoted, Collins plans to use a six-man rotation for one turn.

“We’ll see how those games come out, if somebody happens to be overworked or someone has a short outing, maybe he can come back earlier,” Collins said. “Certainly we have no intentions of jerking anybody out at this time.”

* According to an industry source, the Mets are close to signing first-round draft choice Dominic Smith, whom they selected with the 11th overall pick last week. Smith, an 18-year-old first baseman, has indicated he will attend USC if he does not sign with the Mets.

* Lucas Duda took grounders at first base during pregame drills, but did so on his own. Was Duda trying to send the Mets a subliminal message?

“I was just messing around,” Duda said. “Maybe I shouldn’t have done that.”

Collins confirmed Duda was not instructed to take grounders at first base.

* Collins hasn’t given up on starting Juan Lagares against right-handers, but wanted Kirk Nieuwenhuis in last night’s lineup against Cardinals phenom Shelby Miller. Nieuwenhuis went 0-for-3.

”I’m going to get [Lagares] in, but I’ve got to pick my spots,” Collins said. “And I want to see Nieuwy. He’s had a couple of days off since he came from Vegas after having a great week in Vegas, so I wanted to give him another day to see how he does, but I’m going to get Lagares back in there.”